1. Field of the Invention
The present invention relates to an image forming apparatus, a sheet processing apparatus, and a sheet processing method, and more particularly to an image forming apparatus, a sheet processing apparatus, and a sheet processing method capable of bookbinding by stapling sheets with a simple, compact structure.
2. Description of the Background Art
A background sheet processing apparatus, such as a finisher, is generally connected with an image forming apparatus, such as a copier, a printer, or a facsimile, and has a bookbinding function. As the image forming apparatus becomes more compact and multifunctional, the sheet processing apparatus is also requested to become more compact and to occupy less space when connected with the image forming apparatus.
One example of a background sheet processing apparatus includes first and second tables for loading sheets unstapled and stapled. The first and second tables are adjacent to each other in a sheet conveyance direction. Sheets are delivered onto the first and second tables by rollers, and then aligned, stapled, and stacked on the first and second tables. Each of the first and second tables has a bookbinding function including stapling and a loading function including stacking. However, it is difficult for the sheet processing apparatus including the two tables to have a compact shape.
In another example of a background sheet processing apparatus, one of the first and second tables is smaller than the first and second tables of the above example. Sheets are delivered onto the first and second tables by rollers, and then aligned, stapled, and stacked on the first and second tables as in the above example. The smaller table requires complex structures for finishing functions such as feeding the sheets forward and backward between the first and second tables, shifting and aligning the sheets, and holding the sheets to staple them. For example, a mechanism for driving the rollers to perform the finishing functions becomes more complex and requires more parts, resulting in an increase of manufacturing cost. Moreover, it is difficult to move a stapler for stapling the sheets, resulting in difficulty in stapling two positions on a central edge on the sheets.
Such background sheet processing apparatuses having the bookbinding function have a relatively large body compared to the image forming apparatus and include conveying and aligning systems for conveying and aligning sheets to be stapled as well as a driving system including many mechanisms and parts for driving the conveying and aligning systems. As a result, the background sheet processing apparatuses, which occupy a substantial space and are costly, are not in widespread use.